A comprehensive screening of CB2 receptor ligands revealed extreme functional selectivity, with some drugs activating one cellular pathway while having no effect on another, complicating the development of CB2-targeted therapeutics.
Researchers developing CB2-targeted therapeutics and pharmacologists studying cannabinoid receptor biology.
Classic cannabinoids strongly activated G-proteins but completely failed to recruit arrestins at CB2
What the researchers found
Researchers screened a wide range of CB2 cannabinoid receptor ligands across two signaling pathways: a canonical pathway (inhibition of adenylyl cyclase/G-protein) and a noncanonical pathway (arrestin recruitment).
The results revealed extreme functional selectivity. Classic cannabinoid ligands strongly activated the G-protein pathway but completely failed to recruit arrestins. Most aminoalkylindoles had moderate effects on both pathways. Endocannabinoids were G-protein biased with no arrestin recruitment. One compound (UR144) was arrestin-biased with no significant cyclase inhibition.
Even compounds classified as "antagonists" showed unexpected behavior: AM630 and JTE907 were inverse agonists in the cyclase assay but low-efficacy agonists in the arrestin pathway.
Why it matters
CB2 receptors are promising therapeutic targets (they mediate anti-inflammatory effects without psychoactive effects), but this study shows that the same drug can behave as an agonist in one pathway and have no effect in another. This means conclusions about CB2 function based on one assay may be misleading.
The numbers in context
CP55940 was most potent at both pathways. JWH133 was most efficacious at cyclase. Classic cannabinoids showed zero arrestin recruitment. UR144 was arrestin-biased. Endocannabinoids were G-protein biased.
How the study worked
In vitro pharmacological screening of diverse CB2 receptor ligands in two assay systems: adenylyl cyclase inhibition (G-protein pathway) and beta-arrestin recruitment (noncanonical pathway). Multiple structural classes of compounds were tested.
What this study cannot tell us
All experiments were in vitro and may not perfectly predict in vivo pharmacology. The study used a single cell expression system, and results may differ in cells with different receptor expression levels or signaling environments. The therapeutic implications of pathway bias at CB2 are still theoretical.
How to read the evidence
This is a comprehensive in vitro pharmacological characterization providing strong evidence for functional selectivity at CB2, with implications for drug development.
When this study was published
Published in 2016. The concept of biased agonism has continued to influence cannabinoid drug development strategies.
The bigger picture
Functional selectivity (also called biased agonism) is increasingly recognized across many receptor systems, but the degree of bias seen at CB2 is remarkable. This has major implications for cannabinoid drug development, as a drug's therapeutic or adverse effects may depend on which pathway it preferentially activates.
Questions still open
- Which CB2 signaling pathway mediates the desired anti-inflammatory effects? Could pathway-biased CB2 agonists improve therapeutic outcomes while reducing side effects?
Common questions
What is functional selectivity?
Why does this matter for medicine?
Read the original research
Functional Selectivity of CB2 Cannabinoid Receptor Ligands at a Canonical and Noncanonical Pathway.
The Journal of pharmacology and experimental therapeutics, 358(2), 342-51
Citation
Dhopeshwarkar, Amey; Mackie, Ken. (2016). Functional Selectivity of CB2 Cannabinoid Receptor Ligands at a Canonical and Noncanonical Pathway.. The Journal of pharmacology and experimental therapeutics, 358(2), 342-51. https://doi.org/10.1124/jpet.116.232561
Explore the wider topic
- How THC Affects Your Amygdala: The Brain's Threat Detector and Cannabis
- The Anandamide Connection: Your Body's Natural Bliss Molecule
- How Long for Cannabinoid Receptors to Return to Normal
- Cannabis and the Developing Brain: What Every Teenager (and Parent) Should Know
- Why Can't I Enjoy Anything Without Weed? The Science Behind It
- Dopamine Recovery After Quitting Weed: What the Science Says
- The Endocannabinoid System Explained Simply: What It Does and Why It Matters
- Your Endocannabinoid System Explained: Why Withdrawal Happens
- Your Nervous System After Quitting Weed: Fight or Flight
- Using Weed Under 18: What It Does to Your Developing Brain
- What THC Does to Your Brain: Why Withdrawal Happens
- THC and Your Prefrontal Cortex: What Cannabis Does to Your Decision-Making Brain
- Weed, Cortisol, and Stress: What Cannabis Does to Your Stress Hormones
- Weed and Memory: What the Science Says About THC and Your Hippocampus
- Weed and Motivation: Is Amotivational Syndrome Real?
- Weed and Your Nervous System: What THC Actually Does to Your Brain and Body
- How Weed Rewires Your Reward System (And How to Reset It)